My first cruise, there were only a handful of people at the diaper dash. I just stumbled upon it and thought it was hilarious (though it lasted like 30 seconds with only 2 babies). The next couple cruises, were pretty sparse, too. Last cruise, it was packed, several levels up, though it was a rainy day. I was shocked at how crowded it was.
Also a big fan of the Mickey 500 veggie cars, though we were absolutely terrible at it.